Illusion Reveals How Brain Adapts to Motion

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Watch something in motion, say, a waterfall or scrolling text on
a video game, then look away at a rock, a wall, or anything
stationary. Briefly, the stationary object will appear to move in
the opposite direction.

This visual illusion has been recognized for a very long time;
Aristotle first noted it. Now, a new study has found that even a
very brief glimpse of motion — for as little as 1/40 of a second
— can trigger
the brain mechanism responsible for the illusion.

"It all comes back to a process called adaptation, the idea you
change the sensitivity of your senses based on the environment
you are in, and you do this constantly," said Davis Glasser, the
lead researcher and a graduate student at the University of
Rochester.

For example, when you put your clothes on in the morning, you
only feel them against your skin for a short time, or when you
walk into a room with a noisy air conditioner, you only hear it
for a short time, Glasser explained. It is theorized that
adaptation allows us to ignore a constant stimulus so we can
detect other things, he said.

The visual illusion, called a Motion Aftereffect, is visual
evidence that our brains have adapted to the motion we see. By
looking at a stationary object, we can "read out" this
adaptation, which appears as the illusory motion, according to
Glasser. [ See
the visual illusion ]

Using tests in which participants responded to videos, Glasser
and his colleagues found that after only a very brief exposure to
an image in motion, the brain responds to stationary objects as
if they are actually moving. They found a corresponding pattern
of activity in tests of individual brain cells from a visual
brain region important for perceiving motion.

The motion needed to elicit this response in the human
participants was so brief that the human subjects could not
consciously tell the direction in which it was going. However, it
still affected their perception of a stationary image.

The brevity of exposure to motion needed to stimulate these
responses indicates this process is an automatic adaptation and
can happen anytime you see something moving, according to
Glasser. [ Eye
Tricks: Gallery of Visual Illusions ]

Glasser said he is now exploring the long-standing theory that
adaptation to a particular stimulus, such as motion in our visual
field, improves our sensitivity to other stimuli.